3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas.
Minimization of drive tests (MDT) is a test performed by service providers for coverage optimization by using a user equipment (UE) instead of using a specialized device, such as equipment inside of an automobile. The coverage area of a base station in a mobile communications network varies depending on a location of a base station (BS), deployment of buildings nearby, a user's usage environment, etc. Therefore, it is required for the service providers to periodically perform the drive test, and a lot of costs and resources are consumed. The MDT is used when the service provider measures the coverage by using the UE.
The MDT can be classified into a logged MDT and an immediate MDT. According to the logged MDT, after performing the MDT measurement, the UE delivers a log file containing at least one MDT measurement to a network available at a time of satisfying a reporting condition. According to the immediate MDT, after performing the MDT measurement, the UE delivers the measurement to the network at points in time when a configured reporting condition is satisfied. The logged MDT performs the MDT measurement in a radio resource control (RRC) idle mode, but the immediate MDT performs the MDT measurement in an RRC connected mode.